(a) Field of the Invention
This invention relates to a push-pull type transistor amplifier using complementary transistors and more particularly to an improvement of the signal-to-noise (S/N) ratio and the distortion factor as well as the stability of bias.
(B) Description of the Prior Art
FIG. 1 shows the bias circuit which is conventionally adopted in a complementary push-pull amplifier, wherein the bias voltage sources +E.sub.C and -E.sub.C are connected to the respective bases of complementary transistors Tr1 (NPN type, for example) and Tr2 (PNP type, for example). Transistors Tr1 and Tr2 are connected in push-pull manner between supply voltage sources +E.sub.B and -E.sub.B. Stabilizing resistors Re1 and Re2 are inserted in the emitter circuit of the transistors Tr1 and Tr2 in order to improve the stability of the operating points of the transistors Tr1 and Tr2, i.e., the stability of collector current against the change in ambient temperature. In such a conventional bias circuit, however the insertion of the stabilizing resistors Re1 and Re2 causes the deterioration of the S/N ratio of the amplifier because of the thermal noise produced therein.